Wireless networks are frequently used in industrial process control systems. For example, a process control system often includes sensors that provide measurements over a wireless network and actuators that receive control signals over the wireless network. A process controller can use the measurements from the sensors to generate the control signals for the actuators.
When two nodes in a wireless network are operating at the same power level and have antennas with equal gains, the link qualities in both directions between the nodes are ideally the same. An asymmetric link in a wireless network occurs when a wireless node's uplink and downlink communication qualities are different. An asymmetric link can be formed in various ways, such as due to nodes transmitting at different power levels or environmental factors (like different multi-path reflections). The reliability of a wireless network, such as a mesh network, can degrade severely in the presence of asymmetric links.